A process for producing hydrogen from water has been developed using the sulfur-iodine cycle, sometimes termed a water-splitting process, which utilizes the Bunsen reaction. The process is disclosed in detail in U.S. Pat. No. 4,089,940, which issued on May 16, 1978 to John H. Norman et al., and reacts water, SO.sub.2 and I.sub.2 under conditions which create two liquid phases--an aqueous phase containing the H.sub.2 SO.sub.4 product and a relatively dry phase containing the major portion of the HI product plus iodine and some water. There has been some difficulty in obtaining a relatively dry HI product because HI and H.sub.2 O form an azeotrope. Phosophoric acid has been used to break this azeotrope, as set forth in U.S. Pat. No. 4,127,644, issued Nov. 28, 1978 to John H. Norman et al. Extractive distillation is a somewhat energy-intensive processing step, and the reconcentration of the phosphoric acid is a particularly energy-intensive step.
A further improvement was made with respect to recovery of hydrogen iodide which utilized the high-pressure creation of two separate liquid phases when compositions within certain precentage ranges of HI, I.sub.2 and H.sub.2 O were present, which process is described in detail in co-pending U.S. application Ser. No. 073,566, filed Sept. 7, 1979 in the names of Dennis R. O'Keefe et al. However, effective use of such process generally requires some H.sub.3 PO.sub.4 treatment or the like in order to increase the HI percentages within the composition, again requiring the relatively energy-intensive recovery of the phosphoric acid. Accordingly, the search continued for still less energy-intensive methods for recovering hydrogen iodide.